Security system operated by changes in light at specified locations

ABSTRACT

A security system for the detection of moving targets such as intruders and also of fire and explosions. A plurality of sensors such as photoelectric cells or infrared detectors are focused in an inner and outer pattern, such as pairs of nearly coaxial cones, of different slope, for example, to create inner and outer zones of intrusion. The outputs from the sensors are coupled through a sequencing unit which is programmed to yield an output only when intrusion into the inner zone follows intrusion into the outer zone no more quickly than after a predetermined time delay. A fire detection system places sensors in an area to be protected, utilizing the same general type of operation as the intruder protection with some differences. A plurality of lockout sensors sensing ambient light conditions to lockout the sequencing units of the intrusion detection system and fire detection system if the changes are due to changes in the ambient light.

Akers Jan. 29, 1974 SECURITY SYSTEM OPERATED BY CHANGES IN LIGHT AT SPECIFIED Primary Examiner-John W. Caldwell Assistant Examiner-Robert J. Mooney Attorney, Agent, or Firm-Owen, Wickersham &

LOCATIONS [75] Inventor: Artie E. Akers, Long Beach, Calif. Enckson [73] Assignee: Lawrence Security Inc., San 57 A R Franclsco Cahf' A security system for the detection of moving targets [22] Filed: Dec. 29, 1972 such as intruders and also of fire and explosions. A

plurality of sensors such as photoelectric cells or infra- [211 Appl' 319445 red detectors are focused in an inner and outer pattern, such as pairs of nearly coaxial cones, of different Related Apphcamm Data slope, for example, to create inner and outer zones of n io -impart of Ser. No. 140,808, May 6, intrusion. The outputs from the sensors are coupled 197I- through a sequencing unit which is programmed to yield an output only when intrusion into the inner U-Su Cl- B, one intrusion into the uter zone no more 340/420 quickly than after a predetermined time delay. A fire [5 Cldetection system places sensors in an area to be pro Fleld of Search 340/258 B, 420; 250/221 tected, utilizing the same general type of operation as the intruder protection with some differences. A plu- [561 ci'ed ti iififii ti iifuiilill uiil i iiiififiifiifi UNITED STATES PATENTS detection system and fire detection system if the 3,036,219 5/1962 Thompson 340/258 B changes are due to changes in the ambient light.

19 Claims, 11 Drawing Figures 2o MODE 24 "L l ll SELECTOR 8O 1 A 74 INVERTER L SEQUENCE LOCKOUT SER'ES 22 23 SWITCH UNIT umr LARGE CONE MODE l SELECTOR 78 36 27 OUTPUT MODE 28 TERMINAL 8 I3 SELECTOR 8| INVERTER SERIES 2 3Q SWITCH (SMALL CONE) M MODE SELECTOR 3 32 D MODE A 33 C I5 SELECTOR "2 INVERTER (L o c i fir) /34 f SWITCH I6 MODE 37 l)" SELECTOR LOCKOUT 40 u NIT THRESHOLD A 4| 38 D AMR 44 I'BOMB INVERTER LOGIC SERIES 42 43 SWITCH UNIT OUTPUT I FIRE) l8 THRESHOLD TERMINAL AMP. A '-FIRE SECURITY SYSTEM OPERATED BY CHANGES IN LIGHT AT SPECIFIED LOCATIONS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 140,808 filed May 6, 1971.

BACKGROUND OF THE INVENTION The present invention relates to a security system and more particularly to a security system having transient and ambient change lockout provisions.

Heretofore, intrusion detection systems using the ambient light method of detection were extremely likely to give false alarms, because the light sensors are so sensitive that they see shades of grey which the human eye cannot see. Thus, such systems were too discriminating, signaling intrusions when in fact there were no intrusions. For example, alarms were given when a bird passed through the guarded zone; even a cloud passing over the sun in the daytime would cause enough change in the ambient light to trigger the system. So would a car driving by at night with car lights, or an airplane flying overhead at nighttime.

Another difficulty with prior-art, light-sensitive security systems was that a fire on the premises would activate the lockout circuits. A big flash from a bomb would cause the whole area to light up and would acti vate all systems, but since it would activate the lockout systems, no alarm would be given. It is important to determine whether there is a bomb, a fire, an intrusion, or just passing lightand to discriminate between these different conditions.

Another problem was to provide a long-range security system. Existing security systems are very, very short range. Hypersonic, supersonic, and ultrasonic systems are good for only about feet at the maximum. Radio frequencies are good for only about 30 feet at the most, and beyond these maxima is the range where they give false alarms very readily. An object of the present invention is to extend this range to about 100 to 200 feet, and another object is to make it possible to have systems that look in all directions from one point.

Other security systems have introduced wiring problems, with great lengths of wire being required, and cost problems, due to the expense of installation and the manpower this requires.

Another problem with prior-art security systems has been the cost of providing standby power for the security system. Systems heretofore in use have required relatively large amounts of power, requiring several batteries that cost 60 to 70 dollars each.

There has also been a problem relating to the effect upon the security system by powerlines and the like under certain conditions. Sixty-cycle current and highfrequency current have often in the past actually triggered an alarm system under certain conditions. For example, when somebody put a heavy load on the main powerline and the current dropped, for example, the power and light companies frequently change generators at 2:00 am, and this gives a sudden pulse that has given a false alarm on a nearby security system.

Ease of installation, low power requirements, inexpensive standby systems, systems that will operate under any conditions other than total darkness, and systems free from false alarms are provided by the present invention.

SUMMARY OF THE INVENTION The security system of this invention has a plurality of sensors such as photocells or infrared detectors grouped in clusters with pairs of sensors placed through directing apertures for creating inner and outer zone areas of protection, such as nearly coaxial cones of different slope, for example. The outputs from the sensor clusters are passed through sequencing units, which may be programmed, for example, to yield an output only when an intruder passes into the inner zone after passing through the outer zone and after at least a predetermined time delay, thereby preventing the setting off of false alarms by transient changes within the zones that might be caused by vehicles, birds, etc.

Some sensors may be filtered, and a series of filters may be used varying from heavy filtering to light light or no filtering, for rendering the individual sensors sensitive to change under varying ambient conditions. The sensors receiving minimum filtering may be used for night operation, while the sensors receiving maximum filtering may be used for bright daytime operation.

Alternatively, filters may be replaced with a system providing an automatic'gain for compensating for different types of light.

A series of lockout sensors are provided for sensing surrounding ambient light conditions, their outputs being coupled to the sequencing unit for disabling the sequencing unit during rapid ambient changes such as lightning. These sensors may be omni-directional or directed to the sky, for example.

Another sensor channel can be provided, if desired, for sensing a fire, the only variation being the time delay in the sequencing unit which, because of the nature of the phenomenon, would be longer between the outer and inner zones of interest of protection. A risetime detector may also be provided for eliminating unwanted signals.

An object of the present invention is the provision of an improved security system.

Another object of the invention is the provision of the security system for sensing intruders.

Another object of the invention is the provision of a security system for sensing fires.

Yet another object of the invention is the provision of a security system for sensing both intruders and tires.

A still further object of the invention is the provision of a security system which is not affected by short transient changes.

A still further object of the invention is the provision of a security system which is not affected by rapid ambient variations.

The system of inner and outer cones of surveillance in combination with a sequence operation in which an initial intrusion has to be followed by another intrusion signal, usually from the other cone, before an alarm signal is given, makes sure that if there is an intrusion passing from the outer cone through the inner cone and back out through the outer cone again, an alarm will be sent to the proper authorities. At the same time the system eliminates what is known as glitches, a single pulse coming from any sensor, any amplifier. Signals from birds in flight, clouds over the sun, and so on are eliminated.

The invention, using ambient light, provides an extended range of surveillancesuch as to 200 feet from each sensor cluster.

third floor.

As another example, for a 10 X 100 feet warehouse with no partitions or a 100 X 100 feet open room, the control unit could be installed in one corner, with the sensors mounted on top of the control unit. This would see throughout the whole warehouse or room. Such a system could be prewired, and installation would then be nothing more than putting the sensors in place and plugging the system into live current.

For standby power, the invention can utilize inexpensive batteries costing only about one-half or one-third of what the batteries for other systems cost..

Other objects and many of the attendant advantages of this invention will become apparent with reference to the following detailed description taken into conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a system block diagram of a security system embodying the principles of the present invention.

FIG. 2 is a schematic diagram of one sensor of the embodiment of FIG. 1.

FIG. 3 is a schematic representation of another sensor of the embodiment of FIG. 1.

FIG. 4 is a schematic representation illustrating zone coverage by a plurality of the sensors of the embodiment of FIG. 1.

FIG. 5 illustrates schematically two clusters of sensors of the embodiment of FIG. 1.

FIG. 6 is a schematic representation of a sequence unit and lockout circuits for the device of FIG. 1.

FIG. 7 is a schematic representation of a modified sequencing and lockout circuit for the system of FIG. 1.

FIG. 8 is a block diagram of another security system embodying the principles of the invention.

1 FIG. 9 is a diagram of an area having portions surveyed by fire detecting sensors and portions surveyed by intrusion detectors.

FIG. 10 is a circuit diagram of a threshold amplifier for the fire and bomb detecting and discriminating system.

FIG. 11 is a block diagram explaining the logic unit for the fire and bomb detecting and discriminating sys tem.

DESCRIPTION OF SOME PREFERRED EMBODIMENTS The block diagram of FIG. 1 shows, as an example only, a security embodying the principles of this invention, for detecting intrusions and fires while avoiding false alarms. It has a plurality of sensor clusters 11, 12, 13, 14, 15, 16, 17 and 18. The sensor clusters 11 and 12 are part of a large cone detector system, explained below with reference to FIGS. 3 and 4. The sensor cluster 1 l is coupled through a mode selector 19 and an amplifier 20 to one input of an inverter switch 21. The sensor cluster 12 is coupled through a mode selector 22 and an amplifier 23 to another input of the inverter switch 21. FIG. 5 shows the coupling of the sensor clusters 11 and 12 to the mode selectors 19 and 22, and this feature will be discussed below; it relates also to the coupling of the other sensor clusters to their mode selectors. The inverter switch 21 has an output coupled to a sequence unit 24, which in turn, has an output coupled to an output terminal 25. The sequence units 24 will be explained later in connection with FIG. 6.

The sensor clusters 13 and 14 are part of a small cone detector system explained below with reference to FIGS. 2 and 4. The sensor cluster 13 is coupled through a mode selector 26 and an amplifier 27 to one input of an inverter switch 28. The sensor cluster 14 is coupled through a mode selector 29 and an amplifier 30 to another input of the inverter switch 28. The inverter switch 28 has an output coupled to the sequence unit 24.

The sensor clusters 15 and 16 are part of the lockout system for the device and will be explained below in connection with FIG. 6. The sensor cluster 15 is coupled through a mode selector 31 and an amplifier 32 to one input of an inverter switch 33. The sensor cluster 16 is coupled through a mode selector 34 and an amplifier 35 to another input of the inverter switch 33. The inverter switch 33 has one output coupled to a lockout unit 36 and another output coupled to a lockout unit 37. The lockout unit 36 has an output coupled to the sequence unit 24 and the lockout unit 37 has an output coupled to a logic unit 38.

The sensor clusters 17 and 18 relate to the fire and bomb detection portion of the circuit and will be explained below in connection with FIGS. 9 and 10. No mode selector switch is required. One particular mode is always used. The sensor cluster 17 is coupled through a threshold amplifier 39 and an amplifier 40 to one input of an inverter switch 41. The sensor cluster 18 is coupled through a threshold amplifier 42 and an amplifier 43 to another input of the inverter switch 41. The inverter switch 41 has an output coupled to the logic unit 38, explained further in FIG. 11. The logic unit 38 has an output coupled to an output terminal 44.

A SMALL-CONE SENSOR (FIG. 2)

FIG. 2 shows a sensor 45, which is one'of the sensors of the clusters 13 and 14. The sensor 45 has a light sensing element 46 with output terminals 47 and 48 located within a housing 49. The housing 49 has an aperture 50 at one end thereof. Diverging lines 51 and 52 indicate the cone of surveillance provided by the combination of the sensing element 46, the housing 49, and the aperture 50. They indicate the volume of a zone from which ambient light can pass via the aperture 50 to the sensing element 46. Ambient light from outside the volume defined by the lines 51 and 52 cannot affect the sensing element 46. Since the cone 51,52 is relatively small in angle, it is called a small cone, and the sensor 45 is called a small cone sensor.

Different types of sensing elements 46 may be used, some being more sensitive than others at various points in the visible spectrum. For instance, some systems of this invention use primarily sensing elements 46 housing maximum sensitivity at 5,500 angstroms. However, for operation in artificial light, the system may better use sensing elements 46 whose maximum sensitivity lies at about 6,200 angstroms. Cadmium sulfide and cadmium selenide sensing elements 46 are often preferred, as photoconductive bulk effect cells.

A LARGE-CONE SENSOR (FIG. 3)

FIG. 3 shows a light sensor 53 including another sensing element 46 with output leads 47 and 48 within a housing 54 having an aperture 55 at one end thereof. Diverging lines 56 and 57 define a wider angle than do the lines 51 and 52; so they define a large cone, and the sensor 53 is a large cone sensor. The sensor 53 is one of several sensors used in each cluster 11 and 12. Ambient light from within the cone can affect the sensor 53, and ambient light outside the cone cannot affect A filter 58 is shown here, filtering ambient light. Such a filter may or may not be present in either the sensor 45 (or any other inner-cone filter) or in the sensor 53 (or any other outer-cone filter). The purpose of such a filter, if employed, is to reduce the quantity of light sent to the sensing element 46 and thereby to increase the ability of the sensing element 46 to see light changes in bright light. By having some sensors of a cluster filtered and other unfiltered, the sensitivity range of the cluster can be increased.

LARGE CONE-SMALL CONE COMBINATION (FIG. 4)

FIG. 4 schematically shows a sensor arrangement 60 in which a sensor 45 and a sensor 53 are located closely adjacent to each other and are spacially displaced from another schematically shown sensor 45 and sensor 53. The sensor 53 has an outer zone of surveillance shown schematically by a cone 61 and the sensor 45 has an inner zone of surveillance shown schematically by a cone 62. The sensor 53' has an outer zone of surveillance shown schematically by a cone 63, and the sensor 45 has an inner zone of surveillance shown schematically by a cone 64. The significance of the combination of outer and inner zones has already been alluded to and will be explained later in more detail. The reason for the facing sensor group 45,53 and 45,53 is so that one group can protect another from tampering by someone coming up behind one group.

SENSOR CLUSTERS AND MODE SELECTORS (FIG. 5)

In FIG. 5, a supply voltage is applied at an input terminal 65, there being a ground 66. The input voltage from the terminal 65 passes through a resistance 67 to sensing elements 53,53a and 53b and thence via a resistance 68 to the ground 66. Another path from the input terminal 65 to the ground 66 goes via a resistor 69, sensors 53p, 534; and 53r and a resistor 70.

The sensors 53, 53a and 53b represent the sensor cluster 11. Of course, there may be more or fewer sensors in the cluster 11, but these three give the general idea of clustering sensors. Each sensor can be considered as being substantially identical to the sensor 53 as shown in FIG. 3, either with or without the filter shown there. Similarly, the sensors 53p, 53q and 53r can represent the sensor cluster 12; although again there may be more or fewer sensors. In each instance, the sensor may be like the sensor 53 shown in FIG. 3, with or without the filter.

The mode selector 19 comprises a switch arm 71 and two terminals 72 and 73. The switch arm 71 rests against one of the two terminals 72 and 73 at any one the mode selector switch 71 rests against the terminal 73, while the same increase in light would produce a negative-going signal at the terminal 72. Depending on the situation involved, the user may wish to use either one of these two terminals 72 and 73 to place the system in a desired mode.

The mode selector 22 is substantially identical to the mode selector 19 in structure and is exactly analogous in connection. Thus, there is a switch 75 between two terminals 76 and 77. The terminal 76 is connected between the resistor 69 and the sensor 53p. The second terminal 77 is connected between the sensor 53r and the resistor 70. The switch arm 75 acts to select either a signal which goes positive with an increase in light to the sensors or one which goes negative with the same increase, and a lead 78 connects the switch arm 75 to the amplifier 23.

Each mode selector 19, 22, 26, 29, 31 and 34 thus enables the selection between two signals, one of which is positively actuated by an increase in light and the other of which is positively actuated by a decrease in light. For example, an intruder wearing a dark suit would certainly cause a decrease in the ambient light in the zone, whereas an intruder carrying a flashlight at night would certainly cause an increase. Thus, any mode selector may be changed between night and day, if that is desired.

The connection of each of the mode selectors to its sensor cluster is the same.

SEQUENCING AND LOCKOUT (FIG. 6)

Referring for the moment to FIG. 1, the connections of all the sensor clusters to their respective mode selectors has been explained, and the connection of each mode selector through an amplifier to an inverter switch is apparent. Each of the inverter switches 21, 28, 33 and 41 changes a negative signal to a positive one and passes positive signals.

The present section explains the action of the sequence unit 24 and the lockout unit 31.

A lead 80 (see FIGS. 1 and 6) connects the inverter switch 21 for the A-series system to the sequence unit 24, while a lead 81 connects the inverter switch 28 for the B-series system to the sequence unit 24, The basic idea here is to prevent either the A-series system or the B-series system alone from actuating an alarm. In order for there to be an alarm in the system of FIG. 6, the A system sensors 53, etc., must first indicate an intrusion into one of the large cones 61 (or 63) and then the B system sensors 45, etc., must indicate an intrusion into one of the small cones 62 (or 64). Furthermore, the B intrusion signal must follow the A intrusion by at least a predetermned time interval-for example, no sooner than 4 seconds apart. Still further, the B intrusion signal must follow the A signal within a longer predetermined time interval-for example, before the lapse of 24 seconds. The idea is to prevent false alarms by bodies which move more swiftly than men and by two sporadic bodies. Finally, a lockout unit 41 is connected to the Series C sensor prevents actuation simply by a sudden or gradual change in general ambient light level. (It should be remembered that the Series D sensors are used for fire and explosion detection, and they are treated below in connection with FIG. 9.)

The lead 80 goes to a bus line 82, and when the sensor clusters 11 and 12 give an intrusion signal, there is a momentary flow of current through a relay coil 83 and through a transistor 84, which is also connected to a common bus line 85 that is normally grounded, as will be explained later. In parallel with the relay coil 83 is a diode rectifier 86 which shunts out reverse-flow current through the relay coil 83.

The relay coil 83, when energized throws two switches 83a and 83b. These switches 83a and 83b normally rest against respective terminals 830 and 83d, the terminal 83c being an open circuit. When the relay coil 83 is energized, the switches 83a and 83b rest against the terminals 83e and 83f, respectively, the terminal 83f being an open circuit. The terminal 83d is connected by a lead 87 to the output terminal 25, to give the intrusion alarm. The terminal 83e is connected in between two diodes 88 and 89.

A B-lvoltage input 90 is connected by a lead 91 to the switch 83a; hence when an A-series intrusion signal even momentarily energizes the relay coil 83, the B+ voltage from the input 90 is connected by the switch 83a, terminal 832, the diode 88, and the bus line 82 to the coil 83, latching the coil 83 on, even though the initial actuating signal-the sensed Series A intrusion signalis very brief. Moreover, a resistor 92 connects the bus line 82 to the base of the transistor 84 and keeps it in conductive mode as long as the bus line 82 is supplied by B voltage of the proper polarity, supplying the needed base current. A capacitor 93 shunts any A-C components to the ground bus line 85. Thus, when there is an intrusion signal by the A-series of sensor clusters 11 and 12, passing through the mode selectors 19 and 22 and the amplifiers and 23 to the inverter switch 21, a signal is transmitted via the lead 80 from the inverter switch 21 to the sequence unit 24 which causes the transistor 84 to conduct and to keep conducting. At first, a small base current flows, and then that is multiplied by the transistors gain which may be many times the amount, for example, the gain may be 40.

The instant the transistor 84 starts to conduct, a tim ing capacitor 94 starts to be charged through a fixed timing resistor 95 and a variable timing resistor 96. The variable resistor 96 makes it possible to change the RC time constant provided by the combination of the resistors 95 and 96 with the capacitor 94. For this particular portion of the sequence unit 24 the time constant may be about four seconds, which means that the relay 83 will remain energized for four seconds.

Connected to the capacitor 94 and the resistor 96 is the base of unijunction transistor 97 having one anode connected through a resistor 98 to the bus line 82 and another anode connected to the common bus line 85, which is grounded except where the lockout unit 36 is energized. When the capacitor 94 charges up to where the junction of the resistor 96 and the capacitor 94 has reached the predetermined point set by the characteristics of the particular unijunction transistor 97 that has been picked, then the unijunction transistor 97 fires and discharges its capacity through to ground. The big negative pulse that then results at the junction of the capacitor 94 and the resistor 96 and the base of the transistor 84, then cuts off the transistor 84, deenergizing the relay coil 83 and the switches 83a and 83b then return to the positions shown in FIG. 6.

The diode 89 connects the relay switch terminal 83e to a bus line 100, which is part of a circuit that, except for time constants, substantially duplicates that of the bus line 82. Thus, there is a relay coil 101 in parallel with a diode 102, connecting the bus line 100 to a transistor 103. The relay coil 101 controls switches 101a and 101b, with terminals 101e, 101d, 101e and 101f, the terminals 1010 and 101d being open circuits. The terminal 101e latches the relay 101 energized immediately after the relay 83 closes the switch 83a against the terminal 83e and holds the relay energized after the switch 83a moves away from the terminal 83e, e.g., after the 4-second delay interval determined by the R-C circuit 94, 95 and 96.

A resistor 104 and condenser 105 correspond to the resistor 92 and condenser 93. A timing capacitor 106, a fixed resistor 107 and a variable resistor 108 provide an R-C constant that gives a longer time than do the elements 94, 95 and 96-for example, 24 seconds instead of four seconds. A resistor 109 and a unijunctiontransistor 110 complete this circuit and perform functions like those of their corresponding elements in the other timing circuit.

The purpose is this: to prevent any reaction or any alarm being given even if the A-series sensor clusters 11 and 12 indicate an intrusion unless at least 4 seconds later the B-series of sensor clusters 13 and 14 indicates an intrusion, and to cut the whole thing off if there is no signal from the B-series sensors for a 24 second period. Thus, the relay coil 83 may stay energized for about 4 seconds and the relay coil 101 may stay energized for about 24 seconds. These figures are, of

course, examples but they have actually been found to;

Thus, during the (for example) 24-second period of energization of the coil 101, the lead 81 is connected to the lead 111. However, during the (for example) 4- second period of energization of the coil 83, the lead 111 goes via the switch 83b to the open-circuit terminal 83f. So, a signal from the B-series sensor clusters 13 and 14 during the four-second period following a signal from the A-series sensor clusters 11 and 12.will not initiate a signal. But after the 4-second period, the coil 83 is de-energized, and then the switch moves back to rest against the terminal 83d, connecting the lead 1 l 1 to the lead 87 and therefore to the output terminal 25. Hence, an' intrusion signal from the B-series sensor clusters 13 and 14 which follows more than four seconds after an A-series intrusion signal and within 24 seconds after that signal will sound an intrusion alarm-unless the lockout unit 36 was activated when the A-series signal was given.

The lockout unit 36 is also shown in FIG. 6. The Series D or lockout sensor clusters 15 and 16 may be substantially the same as those of the Series A and B clusters, but are pointed toward a different area. The Series C sensor clusters 15 and 16 are typically pointed to the sky or to some area which gives a general ambient lighting but which does not respond to the area over which the security is being desired; if the signal is the same for the sensors 11, 12, 13, 14, and 16, the lockout unit 36 will be energized and as will be shown, this will prevent the sequence unit 24 from delivering the signal which would otherwise be an alarm signal, to the output terminal 25.

The sensor clusters 15 and 16 give their signals to their respective mode selectors 31 and 34 and to their respective amplifiers 32 and 35 and to the inverter switch 33. The inverter switch 33 sends its output by a line 112 to the lockout unit 36. As shown in FIG. 6, the

lockout unit 36 has exactly the same basic structure as either of the two sequence circuits. Thus, it has a bus line 113, a relay coil 114, a transistor 115, a diode 116, a resistor 117, and a condenser 118 connected to a permanently grounded bus line 119. It has a timing capacitor 120 which is coupled to a fixed resistor 121 and a variable resistor 122 and to a unijunction transistor 123 having one anode connected to a resistor 124 while the other anode is connected to the ground line 119.

The relay coil 114 throws switches 114a and 1141;. The switch 114a latches the relay 114 by moving from a blank terminal 114c to a latching terminal 114e, thereby connecting the B+ input 90 to the relay coil 114 through the lead 91. The switch 1 14b accomplishes the lockout. Normally, the switch 114b rests against the terminal 114d, and it then connects the bus line 85 of the sequence unit 24 to ground, through the bus line 119, where the relay coil 114 is energized, the switch 114b opens this circuit and rests against an open-circuit terminal 1l4f, thereby destroying the connection to ground of the bus line 85, so that the relay 83 cannot be activated, nor can the relay 101. The latching circuit holds the lockout relay 114 on for a desired time, which may typically be from 2 to 4 seconds, depending on the resistance-capacitance characteristics chosen for this particular part of the circuit.

Thus, no intrusion alarm signal can be given if the lockout unit 36 is activated, nor can an intrusion alarm be given during the 4-second (or other appropriate delay period) during which the relay 83 is energized nor can such a signal be given after the delay period (typically 24 seconds), during which the relay 101 is energized. An intrusion signal will sound the alarm only if the Series A sensor clusters 11 and 12 are first energized without energization of the Series C lockout sensor clusters 15 and 16 and if during the time that the relay 83 is de-energized and the relay 101 is still energized there is a second intrusion signal given by the Series B sensor clusters 13 and 14. As a result of this, many causes of false alarms are eliminated from the system. A bird passing through the area would energize both the signal 80 and the signal 81 within the foursecond delay period, so that no alarm would be given. A man walking through would give a completely different result, for he would go from the outer cone to the inner cone in a period that would take longer than 4 seconds. It should also be noted that anything such as lightning flash or passing cloud which would energize both of the signals 80 and 81 simultaneously would not produce an alarm signal.

A MODIFIED FORM OF SEQUENCE CIRCUIT (FIG. 7)

The circuit of FIG. 7 is very similar to that of FIG. 6

and in most particular is identical, so that identical numbers have been used in most of the circuits. The difference in operation is as follows: In the circuit of FIG. 6, the A-series or large-cone sensor clusters 11 and 12 have to be actuated first, and no alarm is given if they are actuated again even during the 20-second active period following the four-second delay. In the FIG. 7 circuit either the A-series or the B-series may be activated first, and an alarm circuit will follow upon either one of them being actuated within the 20-second period following the 4-second delay. (Other times may be used, of course.)

Thus, in FIG. 7 the inputs 80 and 81 are tied together to a lead 125, which goes to the switch 101b where the relay 101 is not energized. The switch 101b rests on the contact 101d, which is connected to the bus line 82 by a lead 126, so that the signals from inputs 80 and 81 will have exactly the same effect. Thus, if there is a primary signal from either the input 80 or the input 81, the

sequence unit 24 will be activated, and nothing will happen if there is another signal from either one of them during the delay period while the relay 83 is energized, which means during the first four seconds. Such a signal energizes the relay coil 101 (via the latching circuits) and therefore moves the switch 101b away from the terminal 101d and against the terminal 101f, whence the lead 91 goes to the switch 83b, which is open during the 4-second delay period. However, after that four-second delay period and before the deactivation period of the relay 101 which may be 24 seconds, another signal from either input or 81 will go via the lead 91 and switch 83b to the lead 87 and give the alarm at the output terminal 25. The circuits being otherwise identical, there is no need to discuss the operation of the lockout unit 36 again, for it is exactly the same as it was before.

A MODIFIED FORM OF DETECTION SYSTEM HAVING A DIFFERENT SENSITIVITY DEPENDING ON THE AMOUNT OF AMBIENT LIGHT FIG. 8 shows a circuit which is basically the same as that of FIG. 1, and the same numbers have been given to the same parts. The differences are that in each one of the circuits one of the sensor clusters is provided with a network that is in parallel with its amplifier.

Thus, the sensor cluster 11 going through the mode selector 19 to the amplifier 20 and then to the inverter switch 21 has, in parallel with the amplifier 20, a parallel network comprising a capacitor and, in parallel with that, a resistor 131 in series with a light sensor 132 the resistance of which drops with an increase in light, as is the case with the sensor 53. Also in parallel with that sensor 132 is a resistor 133. The sensor 132 looks at the same light as a sensor 53 in the sensor cluster.

The resistance of sensor 132 varies from a small amount in bright light (e.g., 1,000 ohms) to a large amount (e.g., 700,000 ohms) in dim light. Since the gain of the amplifier 20 is the ratio of the parallel resistance (the resistance of the network 131, 132 and 133) to the input resistance, the gain will change greatly as the day gets darker and approaches or reaches night. (The capacitor 130 merely routes A-C current around the amplifier 20.) Thus, if R the input resistance is 10,000 ohms, and the resistance of the resistor 131 is 1 ,000,000 ohms, then in bright daylight, when the resistance of the sensor 132 is 1,000 ohms, the gain of the amplifier 20 will be 100.1, while in darker conditions, when the resistance of the sensor 132 is 700,000 ohms, the gain will be 170in both cases excluding the resistor 133. The resistor 133 is used to prevent the development of too much gain, holding it down to perhaps 150 at the most and gives a gain curve more nearly in a straight-line relationship to the light.

This structure obviates the use of filters and yet gives the system increased sensitivity in dim light and in darkness.

FIRE AND BOMB DETECTION AND DISCRIMINATION (FIGS. 9-11) In FIG. 9, sensors a,, a a b,, b and b are intrusion detection sensors corresponding to a sensor cluster 11 (for a,, a and a and to a sensor cluster 12 (for b,, b and b Sensors c,, and c, are fire-and-bomb-detection sensors and correspond to a sensor cluster 17. The sensors c,, c and c while being shown as a total of three sensors, may represent as many as 30 or 40 individual sensors, depending upon the area and volume to be protected.

According to the manufacturer, one cell that can be used as a sensor c,, C or c has a resistance of approximately 15 megohms at 0.01 foot candles of illumination and a resistance of 0.012 megohms at an illumination of 100 foot candles. Actual laboratory measurements of such a cell showed a resistance of 600 ohms under normal lighting (approximately 150 foot candles) and a resistance of 0.8 megohms'when all lights were extinguished.

Fire and bomb explosion detection sensors 0,, c and c (and the sensor clusters 17 and 18) are always installed in the mode whereby an increase in the ambient light, within the area being guarded, produces an increase in the sensor output voltage. This corresponds to the mode wherein the output terminals 73 or 77 are used in FIG. 5, but there is no mode selector switch.

The threshold amplifiers 39 and 42 are always biased such that it requires a signal lighter than the ambient lights to create an output signal. For example, in one system of this invention, the threshold amplifier 39 is always biased 1.1 times maximum ambient while threshold amplifier 42 is always biased 1.3 times maximum ambient.

Suppose that measurements showed that the maximum lighting of a particular area was 1 10 foot candles. Then the minimum resistance attained under ambient conditions by a sensor cell c,, c or a would be in the order of 1,000 ohms.

In FIG. 10, the sensor c, is in a circuit having a 13+ input 140, a resistor R, between the input 140 and the sensor c, and a resistor R between the sensor 0, and ground. If the B+ input is 12 volts and if R, R 1,000 ohms, then that sensor circuit would produce an output signal of four volts when the area was under maximum lighting conditions. The threshold amplifier 39 is set, under these conditions, to require (1.1 X 4) i 4.4 volts for activation, and it will never produce output signals so long as the fluctuations of the ambient lighting remains below the normal maximum, e.g., 110 foot candles.

In the event there is a fire, however, the ambient lighting may increase to 150 foot candles or greater, and the resistance of the sensor 0, would then decrease below 1,000 ohms to, say, about 300 ohms, and the output signal would then be 5.2 volts. Since this signal is greater than the 4.4 volts that bias the threshold amplifier 39, the signal is passed on to the amplifier 40 (FIG. 1 which amplifies that signal and passes it to the electronic switch 41 where it goes on to the logic unit 38 as a fire" signal, and an appropriate alarm signal is emitted.

As the fire increases in intensity it may or it may not produce enough illumination to generate a large enough output voltage to overcome the threshold voltage of a second threshold amplifier 42. Should this occur, the time difference between activation of the threshold amplifiers 39 and 42 enables the logic circuits to determine that it is a fire, not an explosion, and that it is growing in intensity.

Should there be a bomb explosion there will be a tremendous increase in illumination for a very short period (in the order of 15 to 20 milliseconds), and the resistance of sensor clusters 17 and 18 will decrease to values below ohms. Therefore, output voltages will approach 6V, thereby activating both threshold amplifiers 39 and 42 simultaneously. These two signals, arriving at the logic unit 38 at the same time are passed through an AND. gate which produces a positive output indicating that a bomb has exploded.

It is to be understood that the sensors may be connected in parallel as well as in series and, in some instances, it is preferable to use a series-parallel combination.

FIG. 10 is a more detailed interpretation of the fireand-bomb-detection circuitry indicating the threshold amplifier 39, which is just like the threshold amplifier 42 in circuitry. This view illustrates, among other points, why signals of a value less than the signals produced by the sensors at maximum ambient lighting cannot activate the threshold amplifiers 39 and 42, and so are never seen at the input of amplifiers 40 and 43.

In FIG. 10, the sensor cluster 17 is represented by the sensor c,. The sensor 0 is a reference sensor. Between the B+ terminal and ground the two sensors 0, and c are in parallel, with the sensor 0 having a variable resistor R between it and the terminal 140, and a fixed resistor R, between it and ground. The resistor R may be adjusted until the voltage output of the sensor c is identical to that of the sensor c, when they are looking at the same light. The voltage from the sensor 0, is applied through a lead 141 to the plus input of a first amplifier A,, and the voltage output of the sensor c is applied through a lead 142 to the negative input of the amplifier A,. The amplifier A is so structured that a signal applied to its upper negative terminal, as is the case with the lead 142, is inverted in polarity, while the signal applied to its plus terminal, as in the case of the lead 141, produces an output of the same polarity. That is what the minus and plus symbols mean. Thus, if the two signals 141 and 142 are exactly equal, the voltage output from the amplifier A, to the lead 143 will be zero. So long as this adjustment is maintained and so long as the sensors 0, and c, are looking at the same intensity of light there will be no signal output from the amplifier A,.

The amplifier A, has in parallel therewith a capacitor C,, which is a frequency-determining device for amplification, and a gain resistor R,,. It also has 8+ and B- terminals as shown.

The amplifier A, feeds its output via lead 143 to a diode network consisting of diodes D, and D facing in opposite directions. This network gives the system a little leeway, to avoid making the device too responsive, with too great a sensitivity. Because of the diodes D and D there has to be an output fluctuation of greater than at least 0.6 volts in order to break down the voltages on the two diodes D and D and enable conducting to the second amplifier A The purpose is again to help prevent a false alarm from such things as mice running across the floor.

Resistors R and R are load resistors for the amplifier A which again has an upper inverting negative terminal and a lower non-inverting plus terminal and again has a frequency-determining capacitor C and a gain resistor R,,.

The output from the amplifier A is fed to a logic circuit of the kind called a CMOS circuit. The idea is that one obtains a high voltage output from a low voltage input and vice versa. This logic circuit includes two oppositely facing diodes D and D,,, the diode D leading directly to a logic unit B,. The diode D.,, which faces in the opposite direction, is in series with a resistor R and a transistor 0,. The transistor O is provided with a resistor R a resistor R and a biasing resistor R that goes from the base of the transistor Q, to ground. A B+ voltage is applied through the R and R resistances respectively to the base and to the collector of the transistor Q and the emitter is sent to ground. The output signal goes to the logic unit B via a lead 146. Under normal circumstances with no signals from the amplifier A the transistor Q 1 conducts very heavily and gives zero volts through the logic unit. A large negative signal from the lead 145 will cause current to flow down through the diode D through the resistor R and through the resistor R to ground, causing a high negative voltage at the top of the resistor R which completely cuts off the transistor Q,. When the transistor Q, is cut off, no more current flows up to the resistor R to the B+terminal; therefore the junction of the re sistor R and the collector of Q goes immediately to the value of the power supply voltage, which in this case may be around ten volts. This puts a high signal on a pin 151 of the logic unit B The logic unit B has input pins 150 and 151 and an output pin 152, and the logic unit B has input pins 153 and 154 and an output pin 155. These units B and B are CMOS flip-flop generators with low power, CMOS meaning copper-metal-oxide=selenium conductors. The high signal on the pin 15] causes the pin 152 to go to a low voltage, according to the CMOS logic, and that in turn causes the pins 153 and 154 of the logic unit B to go low, and therefore the pin 155 immediately goes to a high output voltage, which is a high signal capable of operating a relay at the output signal 44. The high signal generated at the pin 1550f the unit B is the result of a high negative-going signal out of the amplifier A thus giving one condition.

A positive signal from the amplifier A is passed directly through the diode D tothe pin 150 of the unit B causing that point to go high, and when that point goes high the pin 152 goes low again as a result of the positive signal. Since the pin 152 is tied directly to the pins 153 and 154 of the unit B they both go low, and the voltage at the pin 155 goes high again. So, regardless of what kind of voltage comes out of the amplifier A so long as there is an outpu tthere will be a high signal out of the pin 155 of the unit B Turning now to FIG. 11, when a fire begins and the local lighting increases above ambient to a value greater than 1.] times ambient, the threshold amplifier 39 conducts and causes a signal to appear at the input of amplifier 40. This signal is amplified and a positive signal, greater than 5 volts, is applied to the input of an OR gate 160. The OR gate 160 causes a positive pulse to appear at the output 161 of the OR gate 160. This signal now becomes a pulse to pull in a relay, drop out a relay, or to use in any way to indicate a fire, and it goes to the output terminal 44. The signal at 161 is also used to start a timer 162 approximately 0.] second after the pulse at 161 is generated. This timer 162 generates a negative pulse which is applied to one input of an AND gate 167 and held for 5 minutes, thus inhibiting any signals coming from the bomb detection sensors 18 and the threshold amplifier 42. If the fire increases in intensity, whereby the threshold amplifier 42 is activated within five minutes of detection, the signals from the bomb explosion detection circuits will not pass the AND gate 163, due to the inhibiting signal generated by the timer 162.

Should there be a bomb explosion at the beginning, then both threshold amplifiers 32 and 42 will be activated simultaneously, and positive signals will appear at all inputs of the gate 160 and an OR gate 164, causing positive outputs at 165 and 161. Since timer 162 does not start until the pulse from the output 161 has been present for 0.1 second, there will be a positive signal present at both inputs of the AND gate 163 and a positive signal will appear at an output terminal 166 from the AND gate 163. This will be a positive pulse and can be used as desired to indicate a bomb explosion.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. A security system for the detection of moving targets comprising:

a plurality of sensors focused in inner and outer patterns, the said patterns creating inner and outer zones of intrustion;

a sequence unit having first and second inputs and an output, said first and second inputs coupled to outputs of said sensors and said sequence'unit being operable for producing an output after an input from said outer zone sensor and an input from said inner zone sensor after a predetermined delay.

2. The security system of claim 1 and further including:

a lockout unit, said lockout unit having an input and an output coupled to an inhibit input of said sequence unit; and

at least one lockout sensor disposed in proximity to conditions surrounding said zones of intrusion.

said inner and outer sensors for sensing ambient with an identical variation in light condition within the inner and outer zones of intrusion.

4. The security system of claim 1 wherein:

said inner and outer zones of intrusion comprise substantially coaxial cones.

5. The security system of claim 1 and including:

first and second fire detecting sensors each having an output; and

first and second threshold detectors having inputs coupled to the outputs of first and second fire sensors, respectively, said first and second threshold detectors being set for different levels of detection.

6. The security system of claim 5 and further includ.

ing:

a second sequence unit having first and second inputs coupled to the outputs of said first and second threshold detectors, said sequence unit being programmed for yielding an output after receiving first and second inputs in a predetermined time sequence; and

a second lockout means having an input coupled to at least one said lockout sensor and an output coupled to an inhibit input of said sequence unit.

7. A security system for detecting moving intruders,

including in combination:

an A-series of sensor means for detecting changes in the illumination ofa predetermined field of surveillance and for giving an intrusion signal,

a B-series of similar sensor means having a significantly smaller field of surveillance entirely within that of the sensor means of said A-series and for giving an intrusion signal,

a sequence unit connected to said A-series and having first and second circuits, each including a relay with latching means and relay-operated switches and timing means for retaining the latching of said relay for a predetermined time interval, the time interval for said first circuit being for a relatively brief time and that for said second circuit being for a longer time, an intrusion signal from said A-series activating both said first and second circuits, 'and an alarm output terminal connected by said sequence unit to said B-series through said relay switches when and only when said first circuit has been on. and its time interval has expired and said second circuit is still on during its time interval, whereby said alarm output terminal is energized only when an Aseries intrusion signal is followed by a B-series intrusion signal no sooner than after the expiry of the time interval of said first circuit but during the time interval of said second circuit.

8. The security system of claim 7 having a C-series of sensor means like those of said A-series but having a field of surveillance relating to ambient light rather than a zone to be protected from intrusion,

a lockout unit connected to said C-series and to said sequence unit and having a third circuit like said first and second circuits and having a time interval shorter than that of said first circuit and means energized by a signal from said C-series for disabling a simultaneous intrusion signal from said A-series.

9. The security system of claim 8 having a D-series of sensor means similar to the A-series, threshold amplifier means connected to said D-series for activation only when a predetermined threshold illumination change has been signaled by said D-series,

alarm means activated by said threshold amplifier means for indicating the presence of fire or explosion conditions,

a second lockout unit connected to said C-series and like the other said lockout unit for enabling a simultaneous signal for said D-series.

10. The security system of claim 7 having a D-series of sensor means like those of said A-series, threshold amplifier means connected to saidD-series for activation only when a predetermined threshold illumination change is signaled by said D-series, and

alarm means activated by said threshold amplifier means.

11. The security system of claim 10 having another sequence unit for comparing the signals of two spacedapart sensor means of said D-series, and giving an explosion signal if the two sensor means give simultaneous signals and a fire signal if the sensor means gives its signal a few seconds later than the other said sensor means.

12. A security system for detecting moving intruders, including in combination i an A-series of sensor means for detecting changes in the illumination of a predetermined field of surveillance and for giving an intrusion signal,

a B-series of similar sensor means having a significantly smaller field of surveillance entirely within that of the sensor means of said A-series and for giving an intrusion signal,

a sequence unit connected to said A-series and to said B-series and having first and second circuits, each. including a relay with latching means an relay-operated switch and timing means for retaining the latching of said relay for a time interval, the time interval for said first circuit being for a relatively brief time and that for said second circuit being for a longer time, an intrusion signal from either said A-series or said B-series activating both said first and second circuits, and

an alarm output terminal connected by said sequence unit to said A-series and said B-series through said relay switches when and only when said first circuit has been on and its time interval has expired and said second circuit is still on during its time interval,

whereby said alarm output terminal is energized only when either an A-series or a B-series intrusion signal is followed by another intrusion signal from said A or B series no sooner than after the expiry of the time interval of said first circuit but during the time interval of said second circuit.

13. The security system of claim 12 having a C-series of sensor means like those of said A-series but having field of surveillance relating to ambient light rather than a zone to be protected from intrusion,

a lockout unit connected to said C-series and to said sequence unit and having a third circuit like said first and second circuits and having a time interval shorter than that of said first circuit and means energized by a signal from said C-series for disabling a simultaneous intrusion signal from said A-series.

14. The security system of claim 13 having a D-series of sensor means similar to the A-series, threshold amplifier means connected to said D-series for activation only when a predetermined threshold illumination change has been signaled by said D-series,

alarm means activated by said threshold amplifier means for indicating the presence of fire or explosion conditions,

a second lockout unit connected to said Cseries and like the other said lockout unit for enabling a simultaneous signal for said D-series.

15. The security system of claim 12 having a D-series of sensor means like those of said A-series, threshold amplifier means connected to said D-series for activation only when a predetermined threshold illumination change is signaled by said D-series, and

alarm means activated by said threshold amplifier means.

16. The security system of claim 15 having another sequence unit for comparing the signals of two spacedapart sensor means of said D-series, and giving an explosion signal if the two sensor means give simultaneous signals and a fire signal if the sensor means gives its signal a few seconds later than the other said sensor means.

17. A security system for detecting moving intruders, including in combination an A-series of photoconductive sensor means for detecting changes in the illumination of a predetermined field of surveillance and for giving an electrical intrusion signal,

first mode selector means connected to said A-series for determining whether said intrusion signal is to give positive or negative polarity for a light increase,

first signal amplifying means connected to from said first mode selector means,

a B-series of photoconductive sensor means having a significantly smaller field of surveillance entirely within that of the sensor means of said A-series and for giving an intrusion signal,

second mode selector means, like said first mode selector means, connected to said B-series,

second signal amplifying means connected to said second mode selector means,

a sequence unit connected to said first and second amplifier means and having first and second circuits, each including a latching relay with switches and timing means for retaining the latching of said relay for a predetermined time interval, the time interval for said first circuit being for a relatively brief time and that for said second circuit being for a longer time, an intrusion signal from said amplifying means activating both said first and second circuits, and

an alarm output terminal connected by said sequence unit to at least one said amplifying means through said relay switches when and only when said first circuit has been on and its time interval has expired and said second circuit is still on during its time interval.

18. The security system of claim 17 having a C-series of sensor means like those of said A-series but having field surveillance relating to ambient light rather than a zone to be protected from intrusion,

a lockout unit connected to said C-series and to said sequence unit and having a third circuit like said first and second circuits and having a timeinterval shorter than that of said first circuit and means energized by a signal from said C-series for disabling a simultaneous intrusion signal from said A-series.

19. The security system of claim 17 wherein said amplifying means is in series with a gain resistor and is in parallel with a fixed resistor and a photoconductive sensor surveying ambient light and thereby decreasing its resistance and lowering gain of the amplifying means as ambient light increases and increasing the gain of said amplifying means as the ambient light getsdarker. 

1. A security system for the detection of moving targets comprising: a plurality of sensors focused in inner and outer patterns, the said patterns creating inner and outer zones of intrustion; a sequence unit having first and second inputs and an output, said first and second inputs coupled to outputs of said sensors and said sequence unit being operable for producing an output after an input from said outer zone sensor and an input from said inner zone sensor after a predetermined delay.
 2. The security system of claim 1 and further including: a lockout unit, said lockout unit having an input and an output coupled to an inhibit input of said sequence unit; and at least one lockout sensor disposed in proximity to said inner and outer sensors for sensing ambient conditions surrounding said zones of intrusion.
 3. The security system of claim 1 and further including: a circuit coupled to a first group of said inner and outer zone sensors operable for yielding an output signal of one polarity; and a second group of sensors coupled to a second circuit means for yielding an output of another polarity with an identical variation in light condition within the inner and outer zones of intrusion.
 4. The security system of claim 1 wherein: said inner and outer zones of intrusion comprise substantially coaxial cones.
 5. The security system of claim 1 and including: first and second fire detecting sensors each having an output; and first and second threshold detectors having inputs coupled to the outputs of first and second fire sensors, respectively, said first and second threshold detectors being set for different levels of detection.
 6. The security system of claim 5 and further including: a second sequence unit having first and second inputs coupled to the outputs of said first and second threshold detectors, said sequence unit being programmed for yielding an output after receiving first and second inputs in a predetermined time sequence; and a second lockout means having an input coupled to at least one said lockout sensor and an output coupled to an inhibit input of said sequence unit.
 7. A security system for detecting moving intruders, including in combination: an A-series of sensor means for detecting changes in the illumination of a predetermined field of surveillance and for giving an intrusion signal, a B-series of similar sensor means having a significantly smaller field of surveillance entirely within that of the sensor means of said A-series and for giving an intrusion signal, a sequence unit connected to said A-series and having first and second circuits, each including a relay with latching means and relay-operated switches and timing means for retaining the latching of said relay for a predetermined time interval, the time interval for said first circuit being for a relatively brief time and that for said second circuit being for a longer time, an intrusion signal from said A-series activating both said first and second circuits, and an alarm output terminal connected by said sequence unit to said B-series through said relay switches when and only when said first circuit has been ''''on'''' and its time interval has expired and said second circuit is still ''''on'''' during its time interval, whereby said alarm output terminal is energized only when an A-series intrusion signal is followed by a B-series intrusion signal no sooner than after the expiry of the time interval of said first circuit but during the time interval of said second circuit.
 8. The security system of claim 7 having a C-series of sensor means like those of said A-series but having a field of surveillance relating to ambient light rather than a zone to be protected from intrusion, a lockout unit connected to said C-series and to said sequence unit and having a third circuit like said first and second circuits and having a time interval shorter than that of said first circuit and means energized by a signal from said C-series for disabling a simultaneous intrusion signal from said A-series.
 9. The security system of claim 8 having a D-series of sensor means similar to the A-series, threshold amplifier means connected to said D-series for activation only when a predetermined threshold illumination change has been signaled by said D-series, alarm means activated by said threshold amplifier means for indicating the presence of fire or explosion conditions, a second lockout unit connected to said C-series and like the other said lockout unit for enabling a simultaneous signal for said D-series.
 10. The security system of claim 7 having a D-series of sensor means like those of said A-series, threshold amplifier means connected to said D-series for activation only when a predetermined threshold illumination change is signaled by said D-series, and alarm means activated by said threshold amplifier means.
 11. The security system of claim 10 having another sequence unit for comparing the signals of two spaced-apart sensor means of said D-series, and giving an ''''explosion'''' signal if the two sensor means give simultaneous signals and a ''''fire'''' signal if the sensor means gives its signal a few seconds later than the other said sensor means.
 12. A security system for detecting moving intruders, including in combination an A-series of sensor means for detecting changes in the illumination of a predetermined field of surveillance and for giving an intrusion signal, a B-series of similar sensor means having a significantly smaller field of surveillance entirely within that of the sensor means of said A-series and for giving an intrusion signal, a sequence unit connected to said A-series and to said B-series and having first and second circuits, each including a relay with latching means an relay-operated switch and timing means for retaining the latching of said relay for a time interval, the time interval for said first circuit being for a relatively brief time anD that for said second circuit being for a longer time, an intrusion signal from either said A-series or said B-series activating both said first and second circuits, and an alarm output terminal connected by said sequence unit to said A-series and said B-series through said relay switches when and only when said first circuit has been ''''on'''' and its time interval has expired and said second circuit is still ''''on'''' during its time interval, whereby said alarm output terminal is energized only when either an A-series or a B-series intrusion signal is followed by another intrusion signal from said A or B series no sooner than after the expiry of the time interval of said first circuit but during the time interval of said second circuit.
 13. The security system of claim 12 having a C-series of sensor means like those of said A-series but having field of surveillance relating to ambient light rather than a zone to be protected from intrusion, a lockout unit connected to said C-series and to said sequence unit and having a third circuit like said first and second circuits and having a time interval shorter than that of said first circuit and means energized by a signal from said C-series for disabling a simultaneous intrusion signal from said A-series.
 14. The security system of claim 13 having a D-series of sensor means similar to the A-series, threshold amplifier means connected to said D-series for activation only when a predetermined threshold illumination change has been signaled by said D-series, alarm means activated by said threshold amplifier means for indicating the presence of fire or explosion conditions, a second lockout unit connected to said C-series and like the other said lockout unit for enabling a simultaneous signal for said D-series.
 15. The security system of claim 12 having a D-series of sensor means like those of said A-series, threshold amplifier means connected to said D-series for activation only when a predetermined threshold illumination change is signaled by said D-series, and alarm means activated by said threshold amplifier means.
 16. The security system of claim 15 having another sequence unit for comparing the signals of two spaced-apart sensor means of said D-series, and giving an ''''explosion'''' signal if the two sensor means give simultaneous signals and a ''''fire'''' signal if the sensor means gives its signal a few seconds later than the other said sensor means.
 17. A security system for detecting moving intruders, including in combination an A-series of photoconductive sensor means for detecting changes in the illumination of a predetermined field of surveillance and for giving an electrical intrusion signal, first mode selector means connected to said A-series for determining whether said intrusion signal is to give positive or negative polarity for a light increase, first signal amplifying means connected to from said first mode selector means, a B-series of photoconductive sensor means having a significantly smaller field of surveillance entirely within that of the sensor means of said A-series and for giving an intrusion signal, second mode selector means, like said first mode selector means, connected to said B-series, second signal amplifying means connected to said second mode selector means, a sequence unit connected to said first and second amplifier means and having first and second circuits, each including a latching relay with switches and timing means for retaining the latching of said relay for a predetermined time interval, the time interval for said first circuit being for a relatively brief time and that for said second circuit being for a longer time, an intrusion signal from said amplifying means activating both said first and second circuits, and an alarm output terminal connected by said sequence unit to at least one said amplifying means through said relaY switches when and only when said first circuit has been ''''on'''' and its time interval has expired and said second circuit is still ''''on'''' during its time interval.
 18. The security system of claim 17 having a C-series of sensor means like those of said A-series but having field surveillance relating to ambient light rather than a zone to be protected from intrusion, a lockout unit connected to said C-series and to said sequence unit and having a third circuit like said first and second circuits and having a time interval shorter than that of said first circuit and means energized by a signal from said C-series for disabling a simultaneous intrusion signal from said A-series.
 19. The security system of claim 17 wherein said amplifying means is in series with a gain resistor and is in parallel with a fixed resistor and a photoconductive sensor surveying ambient light and thereby decreasing its resistance and lowering gain of the amplifying means as ambient light increases and increasing the gain of said amplifying means as the ambient light gets darker. 